The advanced imaging-guided approach to acute ischemic stroke in the extended reperfusion time window

Evaluation and treatment of acute ischemic stroke has undergone significant advancement since the 1990s, when acute systemic reperfusion with intravenous alteplase became the first approved method for achieving reperfusion. Until recently, 4.5 h after stroke onset appeared to be the maximum time window in which positive results from thrombolysis can be achieved. However, the advent of advanced imaging modalities, including multimodal magnetic resonance imaging and computed tomography perfusion has allowed clinicians to refine the evaluation of these patients by delineating areas of infarcted tissue, areas of potentially salvageable tissue given timely reperfusion, and areas of benign oligemia. Early work in extending the time window beyond this historical limit of 4.5 h has culminated in four positive trials that demonstrate the benefit of acute mechanical or systemic reperfusion therapy in an extended time window of up to 24 h, using advanced imaging criteria for patient selection. The implications of the success of advanced imaging suggest use of these modalities for disposition decisions and selection of greater numbers of patients for reperfusion but add complexity to individual patient evaluation. Despite this, many questions remain unanswered, including the best choice of thrombolysis agent, whether we can extend the time window further to 24 h, and the optimal combination of mechanical thrombectomy and bridging therapy in the late time window in patients with or without large vessel occlusion.